Input and Output in C (printf() and scanf())

Input and Output (I/O) are essential operations in C programming. The C Standard Library provides functions to read data from the user and display output on the screen.

The header file required for these functions is:

#include <stdio.h>

1. printf() Function (Output)

The printf() function is used to display text, numbers, and variable values on the screen.

Syntax

printf("format string", variable1, variable2, ...);

Example

#include <stdio.h>

int main()
{
    int age = 20;

    printf("Age = %d\n", age);

    return 0;
}

Output

Age = 20

Common Format Specifiers

Format SpecifierData TypeExample
%dInteger (int)25
%fFloat (float)12.50
%lfDouble (double)3.141592
%cCharacter (char)A
%sStringHello
%uUnsigned Integer100
%xHexadecimal1A
%oOctal17

2. scanf() Function (Input)

The scanf() function is used to accept input from the user.

Syntax

scanf("format string", &variable);

Note: Use the address operator (&) with variables in scanf(), except when reading a string into a character array.

Example

#include <stdio.h>

int main()
{
    int age;

    printf("Enter your age: ");
    scanf("%d", &age);

    printf("Your age is %d", age);

    return 0;
}

Sample Output

Enter your age: 21
Your age is 21

Input Different Data Types

#include <stdio.h>

int main()
{
    int age;
    float salary;
    char grade;

    printf("Enter age: ");
    scanf("%d", &age);

    printf("Enter salary: ");
    scanf("%f", &salary);

    printf("Enter grade: ");
    scanf(" %c", &grade);

    printf("\nAge = %d", age);
    printf("\nSalary = %.2f", salary);
    printf("\nGrade = %c", grade);

    return 0;
}

Sample Output

Enter age: 22
Enter salary: 35000.75
Enter grade: A

Age = 22
Salary = 35000.75
Grade = A

Note: The space before %c in scanf(" %c", &grade); skips any leftover whitespace or newline characters.

Reading a String

#include <stdio.h>

int main()
{
    char name[30];

    printf("Enter your name: ");
    scanf("%s", name);

    printf("Hello, %s", name);

    return 0;
}

Sample Output

Enter your name: Rahul
Hello, Rahul

Limitation: scanf("%s", name) reads only one word. To read a full line containing spaces, use fgets().

Example Program

#include <stdio.h>

int main()
{
    int roll;
    char name[30];
    float marks;

    printf("Enter Roll Number: ");
    scanf("%d", &roll);

    printf("Enter Name: ");
    scanf("%s", name);

    printf("Enter Marks: ");
    scanf("%f", &marks);

    printf("\n----- Student Details -----\n");
    printf("Roll Number : %d\n", roll);
    printf("Name        : %s\n", name);
    printf("Marks       : %.2f\n", marks);

    return 0;
}

Sample Output

Enter Roll Number: 101
Enter Name: Amit
Enter Marks: 88.50

----- Student Details -----
Roll Number : 101
Name        : Amit
Marks       : 88.50

Difference Between printf() and scanf()

printf()scanf()
Displays output on the screenReads input from the user
Uses format specifiers to format outputUses format specifiers to interpret input
Does not require & with variablesRequires & for most variables (except strings)

Summary

  • printf() is used to display output.
  • scanf() is used to accept input from the keyboard.
  • Include the <stdio.h> header file to use both functions.
  • Common format specifiers include %d, %f, %lf, %c, and %s.
  • Use the address operator (&) with scanf() for numeric and character variables.
  • Use fgets() instead of scanf("%s") when you need to read a full line of text containing spaces.
Category: MCA

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